MICREL MIC4043BM4 Datasheet

MIC4043 Micrel

MIC4043

Low-Voltage Secondary-Side Shunt Regulator

General Description

The MIC4043 is a shunt regulator optimized for secondary­side regulation in low-voltage power supplies. Featuring an
output stage guaranteed to swing within 400mV of ground,
the MIC4043 can be used in power supplies operating down
to 1.8V, even with optoisolators requiring greater than 1.2V of
headroom.

In power supply applications, the MIC4043 normally drives
the LED of an optically isolated feedback circuit. The MIC4043
monitors a resistively-divided output voltage and sinks error
current through the optoisolator’s LED (secondary side); the
optoisolator’s transistor (primary side) provides this signal to
the controller’s feedback input. The MIC4043 is also practical
for other voltage-monitoring applications requiring an open­collector output.

The MIC4043 replaces conventional ’431-type shunt regula­tors to allow low-voltage applications where there is inad­equate headroom for a 2.5V regulator in series with an
optoisolator. Replacing ’431-type devices requires only a
minor change to the way that the resistive-divider values are
calculated.

Typical Application

Features

• Ideal for 1.8V switching converters

• Low-voltage operation

400mV maximum saturation over
operating temperature range

• Easy to use
voltage in, current out

• 2% voltage tolerance over operating temperature range

Applications

• Optically isolated low-volage power supplies

• Low-voltage discrete regulator control

OPTICAL

ISOLATION

MIC4043

V

IN

MIC38HC43BN

1

2

3

4

COMP
FB
I

SNS

RT/C

T

V

REF

V

V

OUT

GND

8

7

DD

6

5

Low-Side Feedback

Control

1

2

4

3

7

6

PRIMARY SIDE

SECONDARY SIDE

MIC4043

SNKIN

FBGND

V 1.245V

OUT

COMPENSATION

R1

R2

R2





=+

1









R1

V

OUT

Return

200kHz DC-DC Flyback Converter

Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 [phone] • fax + 1 [phone] • http://www.micrel.com

May 2000 1 MIC4043

MIC4043 Micrel

Ordering Information

Part Number Marking Voltage Tolerance Configuration Temperature Range Package

MIC4043BM4 RBAD 1.245V 1% Open Collector –40°C to +85°C SOT-143

Pin Configuration

Pin Description

Pin Number Pin Name Pin Function

1 IN Input: Supply voltage input.
2 SNK Sink (Output): NPN open collector output.
3 GND Ground
4 FB Feedback (Input): 1.245V feedback input from external voltage-divider

FB GND

RBxx

12

IN

MIC4043

network.

34

SNK

Part
Identification

Absolute Maximum Ratings (Note 1)

Input Voltage (VIN) ......................................................+15V

Output Voltage (V

Storage Temperature (TS) ....................... –65°C to +150°C

ESD Rating, Note 3

) ................................................+15V

SNK

Operating Ratings (Note 2)

Input Voltage (VIN) ......................................................+10V

Output Voltage (V
Maximum Output Current (I

Temperature Range (TA) ........................... –40°C to +85°C

) ................................................+10V

SNK

) ................................15mA

SNK

human body model.................................................... 2kV

machine model........................................................200V

MIC4043 2 May 2000

MIC4043 Micrel

Electrical Characteristics

TA = 25°C, bold values indicate –40°C ≤ TA ≤ +85°C; unless noted
Parameter Condition Min Typ Max Units

Reference Voltage 1.245 V
Reference Voltage Tolerance ±1%

±2 %

Supply Current I

Transconductance 1mA < I
∆I

/∆V

SINK

IN

Output Transistor I
Saturation Voltage 400 mV

Output Leakage V

Note 1. Exceeding the absolute maximum rating may damage the device.
Note 2. The device is not guaranteed to function outside its operating rating.
Note 3. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF. Machine model, 200pF.

= 0mA 35 65 µA

SNK

70 µA

< 15mA 3.5 150 S

SNK

2 S

= 15mA 160 250 mV

SNK

= 5V, output transistor off 0.5 µA

SNK

1 µA

Test Circuits

Floating

Bench

Supply

RETURN

Do Not Ground!

V

V8.1k27k33
V5.2k33k33
V3.3k02k33

1k

R

* Compensation element

TUO

1R2R

MIC4043

SNKOUT

IN
GND FB

A

C

FB

2700pF

50Ω

Test Circuit 1. Compensation (Bode Plot) Circuit

Supply

RETURN

1k

MIC4043

IN

SNKOUT

GND FB

* Compensation components

R3
2k

C2*

2700pF

R2
33k

Test Circuit 2. Transient Response Circuit

R1

R1

R2
33k

R

A

C1*
1000pF

Analyzer

R

R

OUTPUT

A

A

May 2000 3 MIC4043

MIC4043 Micrel

Transient Response 1a.

1.8V Output Without Compensation

IN

V

REG

V

OUT

V

V

V

V

IN

REG

OUT

Transient Response 2a.

2.5V Output Without Compensation

IN

V

IN

V

Transient Response 1b.

1.8V Output With Compensation

Transient Response 2b.

2.5V Output With Compensation

V

V

REG

OUT

V

V

V

IN

REG

OUT

Transient Response 3a.

3.3V Output Without Compensation

V

V

V

V

V

REG

OUT

Transient Response 3b.

3.3V Output With Compensation

IN

REG

OUT

MIC4043 4 May 2000